Synthetically produced amorphous silicas play an important role as an ingredient in many of today's toothpaste formulations. In addition to their cleaning ability, they are also relatively safe, nontoxic, and compatible with other toothpaste ingredients, including glycerin, sorbitol (or xylitol), thickening agents, detergents coloring and fragrance materials and, optionally, fluoride containing compositions.
Synthetic precipitated silicas are prepared by admixing dilute alkali silicate solutions with strong aqueous mineral acids under conditions where aggregation to the sol and gel cannot occur, stirring and then filtering out the precipitated silica. The resulting precipitate is next washed, dried and comminuted to desired size.
Silica gels include silica hydrogels, hydrous gels, aerogels, and xerogels. Silica gels are also formed by reacting alkali silicate solutions with strong acids to form a hydrosol and aging the newly formed hydrosol to form the hydrogel. The hydrogel is then washed, dried and comminuted as described above.
When preparing synthetic silicas, the objective is to obtain silicas which provide maximal cleaning with minimal damage to oral tissue. Dental researchers are continually concerned with identifying precipitated silicas meeting these objectives.
Examples of precipitated silicas described in the art include U.S. Pat. No. 4,122,161 to Wason, Oct. 24, 1978, U.S. Pat. Nos. 4,992,251 and 5,035,879 to Aldcroft et al., Feb. 12, 1991 and Jul. 30, 1991 respectively, U.S. Pat. No. 5,098,695 to Newton et al., Mar. 24, 1992, and U.S. Pat. No. 5,279,815 to Wason et al., Jan. 18, 1994. Similarly, silica gels have also been described in the art as demonstrated by U.S. Pat. No. 4303,641, Dec. 1, 1981, to DeWolf, II et al., U.S. Pat. No. 4,153,680, May 8, 1979, to Seybert, and U.S. Pat. No. 3,538,230, Nov. 3, 1970, to Pader et al.
Moreover, various combinations of silicas have been described in the art. Silica combinations involving compositions of differing particle sizes and specific surface areas are disclosed in U.S. Pat. No. 3,577,521. to Karlheinz Scheller et al., May 4, 1971 and U.S. Pat. No. 4,618,488 to Macyarea et al., Oct. 21, 1986, respectively. Similarly, U.S. Pat. Nos. 5,110,574 to Reinhardt et al., May 5, 1992 discloses combining precipitated thickener and polishing silicas to form silica compositions having oil absorption values of al least 200. Further examples of silica combinations include U.S. Pat. No. 5,124,143 to Muhlemann, Jun. 23, 1992 and U.S. Pat. No. 4,632,826 to Ploger et al., Dec. 30, 1986.
While the prior art discloses a variety of silica compositions useful as dental cleaning abrasives, there is still a need for additional compositions providing improved cleaning with minimal abrasion. The present inventor has discovered amorphous silica abrasive compositions comprising precipitated and gel silicas providing improved dental cleaning with minimal abrasion.
Accordingly, it is the object of the present invention to provide a precipitated silica and gel silica compositions providing improved pellide cleaning without a corresponding increase in dentin or enamel abrasion. Another object of the present invention is to provide an improved method for the prevention or removal tooth stains. A further object of the present invention is to provide an improved method for the prevention or removal of plaque. These and other objects will become readily apparent from the disclosure which follows.